It has been conventional practice to support mine roofs with spaced support plates in order to prevent roof falls and roof fall accidents. Such support plates are generally held flush against the roof of the mine by long bolts or anchors that are inserted into bore holes drilled into the mine roof and fixed therein by mechanical or resin anchoring means.
Where resin anchoring means are used to fix a bolt or rod that supports a mine roof support plate, usually a sleeve is inserted into the bore hole and a threaded bolt is threadedly engaged with the sleeve to support the plate. This has led to the use of various stop members on the bolts or anchors to enable initial rotation of the anchor to burst a resin cartridge previously inserted into the bore hole and enable mixing and setting of the resin to adhesively secure the anchor and a subsequent rotation of the rod to overcome the affect of the stop member, and thread the bolt into the anchor and pull the support plate flush against the mine roof. Such systems, where an anchor sleeve and bolt are both provided, require the formation and machining of dual complex parts and close tolerances between the coacting parts in order to effectively provide for meshing of the various parts and application of the correct torque to the bolt in order to assure safe and secure fixation of the support plate to the roof. Examples of such anchor and bolt systems are shown in U.S. Pat. Nos. 3,877,235, 4,023,373 and 4,122,681 which discuss the coaction of the bolt and anchor as well as the problems associated with, and the need for, strengthening of mine roofs.
Some existing anchors comprise a concrete reinforcing bar having a head and flange on one end that is inserted into a bore hole and adhesively secured therein to support a plate. In another type of anchor bolt where no sleeve is required, a problem exists in assuring that the bolt will be firmly secured within a bore hole and also that the support plate will be fixed flush to the roof of the mine. For example, in U.S. Pat No. 3,940,941, a method for reinforcing roofs is disclosed wherein a metallic bolt is threaded at its lower end, and the upper end has a transverse cut at the top to form a pair of teeth to aid in piercing the resin packages. The threaded portion at the lower end of the bolt has a discontinuity therein so as to enable counterclockwise rotation of the bolt to advance the same into the bore hole and disperse the resin and fix the bolt in the bore hole, and clockwise rotation of a nut on the bolt to thread the nut upwardly and pull a washer carried thereon flush with the roof structure. A dual step operation is required to affix the washer flush with the mine roof, using counterclockwise and then clockwise rotation, and a depending portion of the threaded section remains exposed and extending downwardly from the roof, which could present a safety hazard in low roof areas of a mine.
It is an object of the present invention to provide a unitary mine roof support plate bolt that does not require coaction or relative movement between parts of the bolt system.
It is another object of the present invention to provide a mine roof support plate bolt that requires only a single operation to adhesively fix the bolt into a bore hole and fix a support plate flush with the roof surface.
It is a further object of the present invention to provide a mine roof suppport plate bolt that assures adhesion of the upper section of the bolt within a bore hole by retention of resin adjacent that upper section during insertion and rotation of the bolt into the bore hole.
It is an even further object of the present invention to provide a mine roof support plate bolt which will enable the use of the bolt in bore holes that may be slightly less in depth than that required to accept the bolt and enable pulling of the support plate flush with the mine roof.